It is very important to wash your deck before you apply anything to it. It depends on what you are going to apply to your deck as what to what from of application you use. The product you go with give you the best way to apply it. This is a good time of year to do this type of project but if are getting heavy dews in your area be sure to stop at around 3pm to give product time to dry before the dew settles on it during the night.